Polyethylene is a commodity plastic material, and has been used for a variety of consumer applications such as milk containers, commercial drum liners, disposable garbage bags, etc. In addition, a form of polyethylene known as polyethylene foam has been manufactured, which makes use of the established properties of polyethylene, but in a reduced density format. In addition, polyethylene foam has been crosslinked, to improve its durability in a given application. For example, crosslinked polyethylene foam has been used for such applications as exercise mats and as a protective layer in plastic helmets.
As noted above, the present invention is directed at an integrally shaped crosslinked polyethylene foam box, wherein an extremely durable integrally shaped hinge has been produced, which is capable of repeated articulation, without failure. The uniqueness of this invention, as more fully explained herein, lies in the fact that the crosslinked polyethylene foam has been reduced to very narrow dimensions at the hinge area, but unlike most crosslinked materials which tend to be brittle and particularly sensitive to repeated stress, the hinge material of the present invention maintains tremendous flexibility over extended use periods.
of course, the prior art describes a variety of packaging articles formed from foam materials, but none describes the novel features of the present invention.
As a prime example, in U.S. Pat. No. 4,885,820, there is described the use of a hinge for joining surfaces of sheet material which comprises a strip of film or foam laminate positioned with a foam layer across the surfaces to be joined. The foam layer is tackified by heating and pressure is applied to the strip, thus heat sealing the strip to the surfaces. The hinge strip is preferably polyethylene film laminated to polyethylene foam and the surfaces to be joined may be polyethylene foam or a film/foam laminate. The significance of this disclosure is that until only recently, the prior art suggested that in the case of polyethylene foam, a separate hinge joint was necessary to join foam sheets in order to prepare a working hinge element.
Other related prior art includes U.S. Pat. No. 4,848,543 which describes a thermally insulated disposable container for food items, which was formed of a unitary sheet of plastic foam material whose lower and upper sections each form with a round flat member and a drafted side wall. An integrally shaped flexible hinge was said to connect the portion of the rim of each of the upper and lower sections, so that the sections could be closed with the food items contained inside. However, this particular integrally shaped foam box was formed from a unitary sheet of polystyrene foam (which is not crosslinked). Moreover, this disclosure fails to teach or suggest that the crosslinked polyethylene foam can be pressed into a reduced thickness hinge element that is capable of repeated flexing.
Other related prior art appears in U.S. Pat. No. 4,382,536, which like the '543 patent, employs polystyrene, but which reports the preparation of an egg carton (with a non-expanded skin on one side) including an integrally formed cover and tray portions interconnected together by a pair of hinges adjacent opposite sides of a hinge band. In particular, the '536 patent described that thin resiliently bendable flaps for cushioning eggs in the carton had not been prepared from polystyrene because of perceived limitations on the capabilities of thermo-molding polystyrene material. The '536 patent goes on to state that in accordance with the invention described therein, it had been found that a thin polystyrene flap for cushioning eggs could be thermo-formed utilizing a sheet of polystyrene with a non-expanded skin on one side. The '536 patent emphasizes that the polystyrene sheet with the skin side facing the male section of the mold is pressed between the male and female mold members, wherein the flap hinge becomes essentially the skin portion of the polystyrene sheet without the expanded foam layer thereon. In addition, the '536 patent emphasizes that the minimum gap between the mold sections which form the flap hinge was in the range of about 0.005 inches to 0.011 inches.
In U.S. Pat. No. 4,298,133 there is described a foam plastic disposable tray and cover typically used for takeout dinners at fast food establishments. The tray and cover were said to be joined by an integral hinge along one side edge. However, in a manner similar to U.S. Pat. No. 4,382,536, there was no teaching regarding a reduction in thickness of the foam at the hinge region.
More recently, in U.S. Pat. No. 5,183,159, there is described a reusable container for packaging objects for shipping. The container was said to comprise a pair of outer frame members having a clamshell configuration in which the two frame members were connected by a reclosable hinge of the same thickness as the box. The hinge was said to be designed to permit articulation between an open and closed position, and those plastic materials which were described as suitable were polymers and copolymers such as polyvinyl chloride, polyethylene terethalate (PET), polyethylene terethalate/glycol modified (PETG) and PVC PET or PETG copolymers. Crosslinked polyethylene foam is not mentioned, and in addition, it should be noted that the '159 patent, with respect to the polymers mentioned above, was concerned with the use of such polymers in non-foam or film form.
Accordingly, the principal object of the present invention is to provide an integrally shaped flexible crosslinked foam container which is equipped with an integrally shaped hinge, which is capable of repeated articulation without failure.
Another object of this invention is to provide a method for manufacturing an integrally shaped flexible crosslinked foam container, by essentially a single-step manufacturing process wherein the crosslinked foam is heated to a desired temperature and pressed into container configuration, said container containing an integrally shaped hinge section, the hinge section comprising a reduced thickness hinge element capable of repeated flexing.
A still further object of this invention is to provide an integrally shaped crosslinked foam box, prepared from flexible crosslinked polyethylene, optionally including a fabric coating, which in combination with the integrally shaped hinge, provides essentially unlimited repeated articulation at the hinge section (opening and closing) without failure due to repeated stress.